Practice
Ms. Harmon is rearranging the classroom. You volunteer to help move her desk to the other side of the room. You push the desk with a horizontal force of 84 N and move the desk 12 m. How much work did you do?
1008 j
What is the formula used for work?
W=Fd
An electric blanket warms a bed on a chilly night.
electrical energy changes to thermal energy
Energy due to motion
Kinetic Energy
Which unit is used to measure energy?
joules (j)
A crate weighs 1620 N. If you can use a pulley system to lift that crate with a force of only 135 N, then what is the mechanical advantage of the pulley system?
12
What is the formula for mechanical advantage?
MA= output force/ input force
A cowboy is riding his horse through town. Where did their energy come from?
The food they eat
Energy that is stored due to the interactions between objects
Potential Energy
Which unit is used to measure force?
Newtons (N)
A 2 kg apple is hanging from a tree 3.5 m above the ground. What is the gravitational potential energy of the Earth-apple system relative to the ground?
68.6 j
What is the formula for gravitational potential energy?
GPE=mgh
A walnut falls to the ground from a lofty branch on a walnut tree.
GPE becomes kinetic energy
Energy that is stored by compressing, stretching, or bending an object
Elastic Potential Energy
Which unit is used to measure efficiency?
Percent (%)
You do 78 J of work pushing a box up a ramp. If the output work from the inclined plane is 13 J, then what is the efficiency of the inclined plane?
16.7%
What is the formula for efficiency?
e = output work/ input work x 100
An athlete eats a bowl of pasta, then rides in a bicycle race
Chemical potential energy becomes kinetic energy
Energy that is due to chemical bonds
Chemical Potential Energy
Which unit is used to measure Power?
Watts
If a runner’s power is 400 W as she runs, how much chemical energy does she convert into other forms in 10.0 minutes?
4,000 j
What is the formula for kinetic energy?
KE = 1/2 mv2
A car engine starts
chemical potential energy changes to mechanical energy
Energy that is due to the gravitational forces between objects
Gravitational Potential Energy (GPE)
Which unit is used to measure mechanical advantage?
There is no unit for this